1. Technical Field
The invention generally relates to methods of detecting anomalies in ambient alternating current (AC) fields.
2. Description of the Related Art
The prior art teaches various methods of detecting anomalies in ambient direct current (DC) fields. For example, the prior art teaches the use of magnetic field sensors, commonly referred to as magnetic anomaly detectors (MAD), to detect distortions in the earth's DC magnetic field caused by ferromagnetic objects. These types of sensors are typically limited by the dynamic range of the magnetic sensor and/or geomagnetic noise.
The prior art also teaches the use of detecting anomalies in ambient DC fields using electric field sensors. These sensors detect distortions in the earth's DC electric field caused by conducting objects, such as unarmed intruders and/or aircraft that do not include any ferromagnetic components. Unfortunately, alternating current (AC) electric fields generated by 60 Hertz (Hz) AC power lines (typically referred to as 60-Hz power line “hum”) interfere with these types of sensors and make it more difficult to detect anomalies in the earth's DC electric field.